What did the English ever do for us? Unlike the Romans in The Life of Brian, not much in the way of aqueducts or wine. But even the stoutest anti-imperialist in any former British colony has to admit that the empire left us a rather wonderful language. The Man Booker prize may be one of the last shadows of that empire, evoking as it does an imagined community unchanged since 1921, when Irish independence began its demise. But the 2013 shortlist is startling evidence of what happened to the language the empire left behind. It is the great triumph of British culture – because it no longer belongs to Britain.

There is nothing new, of course, about the Man Booker list featuring novelists from the former colonies. This year's list, though, makes a definitive statement that such writers are no longer the exotic outsiders that add colour (literally as well as figuratively) to the British norm. They are the new normal.

There is one English writer on the list, the splendid Jim Crace. He takes his place alongside a Zimbabwean (NoViolet Bulawayo), an Anglo-Indian American (Jhumpa Lahiri), a New Zealander (Eleanor Catton), a Canadian-Japanese American (Ruth Ozeki) and an Irishman (Colm Tóibín). There's an element of the arbitrary about such lists, but this one does feel significant. It marks the death of two big narratives about language in general and English in particular.

From the 18th century onwards, there was the notion of "proper" English, an idea that expressed itself in pedantry about grammar and pronunciation but that was always about power and control. We can see it at work through, for example, Samuel Johnson and his protege James Boswell. Reviewing Johnson's dictionary, Lord Chesterfield wrote that the English language was in "a state of anarchy" and required the firm smack of discipline: "Toleration, adoption and naturalisation have run their lengths. Good order and authority are now necessary… We must have recourse to the old Roman expedient in times of confusion and choose a dictator."

That the dictating would be done by the English ruling class went without saying. Boswell, meanwhile, had to learn how to speak his own native language: he took elocution lessons before leaving Scotland for London in order to acquire "a mode of speaking to which Englishmen do not deny the praise of elegance". The English upper class owned the language as surely as it owned the great estates.

It has taken a long time for these attitudes to be banished to the margins occupied by ranting cranks. The idea that an English elite was the rightful possessor of the language and governed its proper use was powerful enough to haunt even James Joyce, arguably the greatest re-inventor of English since Shakespeare.

In A Portrait of the Artist as a Young Man, his alter ego Stephen, who is Irish, is disturbed by a conversation about words with an English priest: "The language in which we are speaking is his before it is mine. How different are the words home, Christ, ale, master, on his lips and on mine! I cannot speak or write these words without unrest of spirit. His language, so familiar and so foreign, will always be for me an acquired speech. I have not made or accepted its words. My voice holds them at bay. My soul frets in the shadow of his language." Writers from the wider empire, as well as from the "wrong" parts of Britain, could have written the same.

That anxiety is all but gone. The souls of Bulawayo or Lahiri or Ozeki surely don't fret in the shadow of London middle-class English. Tóibín and Catton hardly read Crace (or Shakespeare, Austen or Dickens) and feel that the riches of English are "his before they are mine". This is equally so, of course, within Britain itself – at least in the literary sphere, the authority of Lord Chesterfield's dictators has been overthrown. Chesterfield was wrong: "toleration, adoption and naturalisation" had not run their course. They had vast new fields to play in, many of them in Asia and Africa.

But another idea has unravelled, too, and it was one that had deeper roots in the empire's outposts than at the heart of power. Through the 19th century and for much of the 20th, it was commonplace to believe that subject peoples could never throw off the yoke of empire unless they abandoned the language of the imperial oppressor. It seemed obvious to anti-colonial revolutionaries everywhere that there could be no such thing as a free and independent culture that had English at its heart. The greatest compliment to English is that it proved to be just too damned attractive for this idea to be maintained, even by those who had good reason to hate England.

The most obvious case in point is my own country, Ireland. Most of those who led the Irish revolution believed passionately that Irish independence simply wouldn't be worth having if it did not lead to a revival of the Gaelic language as the vernacular in Ireland. The state they created made Gaelic compulsory and insisted that it must be the "first official language".

The project failed completely, not just because English was so useful for a country of emigrants but also because most of the leading Irish writers, from Yeats to Heaney, continued to find English too rich and too beautiful to be dispensed with. The same, over time, has proven to be true in Scotland (where the great poet and visceral nationalist Hugh MacDiarmid started out insisting he would write only in Scots and ended up writing in English in spite of himself), India, Nigeria, and elsewhere. The idea that free countries couldn't have their own distinctive literatures in English turned out to be wildly mistaken.

What the would-be linguistic dictators called the "anarchy" of the English language has been redefined by writers from the greater anglophone world as its great generosity. Its glory is that it lets everyone in without making them all the same. English was multicultural long before it contained that word. Because it is itself an unruly bastard tongue, it is capacious enough for everyone to find within it their own unique cadences. The England that once had pretensions to govern this glorious tongue is gone. The tongue itself is taking infinite new shapes in billions of mouths. As we lowered the Union flag and waved off the last governors, we who were once ruled from London had to take our hats off and say: "So long and thanks for all the words."